Nobiletin and tangeretin belong to a class of polymethoxyflavonoids that are included in citrus fruits. Nobiletin has a structure represented by the following formula (I). Tangeretin has a structure represented by the following formula (II). Nobiletin and tangeretin are said to have various pharmacological actions such as a carcinogenesis suppressing action, a blood sugar level inhibiting action, and a preventive effect for Alzheimer type dementia.

Citrus fruits such as ponkan and Taiwan tangerine are used as raw materials for the processing of juices, jams and the like in many cases. When citrus fruits are subjected to such processing, mainly the fruit pulp is utilized, and the fruit pulp left over from juice extraction or fruit peel is disposed of as juice waste. However, nobiletin and tangeretin are included in larger amounts in such juice waste than in the juice pulp. A portion of the juice waste of citrus fruit is reutilized for the extraction of essential oil or as feeds for livestock; however, the juice waste of citrus fruit is not expected as a raw material for a food product material containing nobiletin and tangeretin.
JP 2005-145824 A (hereinafter, referred to as “Patent Document 1”; the descriptions of the Patent Document 1 are incorporated herein by reference) describes a method for obtaining nobiletin by the steps of extracting thinned fruits of ponkan with 30% ethanol under reflux for 1 hour, extracting and concentrating a residue thus obtained with hot water at 90° C. or higher for 1 hour, decanting the concentrate to obtain a supernatant, passing this supernatant through a porous adsorption resin, and then eluting nobiletin with 70% ethanol.
Furthermore, JP 2006-327998 A (hereinafter, referred to as “Patent Document 2”; the descriptions of the Patent Document 2 are incorporated herein by reference) discloses a method of manufacturing polymethoxyflavonoids including nobiletin and tangeretin by the steps of obtaining a pot bottom oil by distilling the fruit peel oil of oranges under reduced pressure to remove limonene, subjecting this pot bottom oil to thin film distillation, subsequently adding about a 25-fold volume of 70% ethanol, and then heating the mixture to reflux.
Also, known as products that are currently commercially available are products sold by ARKRAY, Inc. (see Non-Patent Document 1; the descriptions of the Non-Patent Document 1 are incorporated herein by reference).